18 CONCHOLOGIA CESTRICA. 
Order PULMONIFERA. 
Terrestrial, or sub-aquatic animals, which respire free 
air, through an opening in or under the right side of the 
mantle. In some of the families of this order, the animal 
is furnished with a testaceous or horny plate, the opercu- 
/um, attached to the posterior part of the foot. When 
the animal retires within the shell, the posterior half of 
the body is folded on the anterior, resembling in its 
action the shutting of a clasp-knife, after which, the head 
and body are withdrawn, leaving the operculum, which 
is situated on the posterior part of the foot, to close the 
aperture. 
Sub-order GEOPHILA. 
Animal, terrestrial, tentacles four, retractile by inver- 
sion, or contractile with the head beneath the mantle; 
upper pair long, cylindrical, ending in bulbs, which con- 
tain the eyes ; lower ones short, or obsolete ; ske// mostly 
spiral. 
INOPERCULATA. 
The operculum wanting. 
Family PHILOMYCENID&. 
The Slugs. 
Mantle covering the entire upper surface of the animal. 
Shell entirely wanting. 
DIAGRAM OF THE GENERA AND SPECIES OF THE FAMILY PHILO- 
MYCENID, 
FAMILY, f§ Genus, TEBEN NOPHORUS. Carolinensis, 
{ Spectes, 
PHILOMYCENID. (Sun-cenus, PALLIFERA. 
orsalis. 
Oss. — The slugs, or naked snails, have many charac- 
ters common to the true snails; both are nocturnal in 
